It may be desirable for an engine to include a turbocharger and exhaust gas recirculation (EGR) to reduce emissions of NOX, CO, and other gasses and to improve fuel economy. An EGR system may include a low pressure exhaust gas recirculation (LP-EGR) system, a high pressure exhaust gas recirculation (HP-EGR) system, or both a LP-EGR and a HP-EGR system, for example. The amount of EGR routed through the EGR system is measured and adjusted during engine operation to maintain desirable combustion stability of the engine. One solution for measuring the amount of EGR in the LP-EGR system is for the LP-EGR system to include a mass air flow (MAF) sensor downstream of the hot, moist, exhaust gasses and upstream of the turbocharger compressor. However, the MAF sensor may be exposed to high exhaust temperatures, high concentrations of soot and exhaust hydrocarbons, water condensation, and exhaust pulsations. These conditions may reduce the lifetime of the MAF sensor and reduce its accuracy when measuring the EGR rate. Additionally, a dual bank engine may include two MAF sensors, increasing the engine's cost.
The inventors herein have recognized the above issues and have devised an approach to at least partially address them. For example, the amount of EGR in the LP-EGR system may be resolved by measuring flows at multiple other, cooler and drier locations of the engine intake (e.g., before and after EGR introduction), where the gasses include lower concentrations of soot and exhaust hydrocarbons, and the gasses are less affected by exhaust pulsations.
In one example, a method for controlling an engine is disclosed. Low-pressure EGR is delivered downstream of an intake throttle and upstream of a turbocharger compressor. Further, an operating parameter is adjusted based on an EGR mass flow identified from a difference between a measured clean air mass flow entering the intake throttle and a total mass flow measured downstream from the turbocharger compressor. In this manner, the EGR rate may be measured and maintained at a desirable level while a MAF sensor may be exposed to lower temperatures, lower concentrations of soot and exhaust hydrocarbons, less water condensation, and fewer exhaust pulsations. Thus, the MAF sensor may potentially have a longer lifetime and greater accuracy.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.